The time-honored method for plating tin-lead alloys, commonly called Solder Plate, is to have these two metals present in solution as fluoborates with an excess of fluoboric acid and boric acid. In order to obtain smoother deposits, it is common to add various types of proteins, such as peptones, glue, gelatin or meat proteins. The fluoborate-based bath containing peptone is most commonly used and it is commercially successful in obtaining smooth matte deposits. Brighter tin-lead solder deposits can be obtained from these fluoroborate based baths by adding various brightening agents, such as aromatic aldehydes, pyridine compounds, ethylene oxide wetting agents and formaldehyde.
The main problem with these fluoborate-based baths is the fluoborate ion itself. Fluoborates are not only highly poisonous but are also highly corrosive to the equipment used in the plating environment. Fluoborates are also difficult to remove from the waste water that follows the plating operation and presents a serious problem for the waste-disposal engineer.
Alkane or alkyl sulfonic acids containing 1 to 5 carbon atoms in the alkyl group have previously been used in electrolytic plating baths. See, for example, U.S. Pat. No. 2,525,942 to Proell.
Alkanolsulfonates, phenolsulfonates and cresolsulfonates have also been used in electroplating baths. See, for example, the article entitled ELECTRODEPOSITION OF BRIGHT TIN-LEAD ALLOYS FROM ALKANOLSULFONATE BATH by N. Dohi and K. Obata, Proceedings of Interfinish 80, as well as U.S. Pat. Nos. 4,132,610 and 3,905,878.
U.S. Pat. No. 4,459,185 to Obata el al. discloses alkyl or alkanol sulfonic acid baths for plating tin, lead, or tin-lead alloys. These baths contain at least one cationic, amphoteric or nonionic surfactant along with a levelling agent.
None of the prior art, however, discloses the applicant's novel methods for preparing tin-lead electrolytes. Furthermore, none of the prior art recognized the addition of various additives for specific purposes, as is disclosed hereinbelow.